1. Field of the Invention
The present invention relates to a method for diffusing a treating agent into a medium and an apparatus used therefor, a method for injecting a liquid into a medium and an apparatus used therefor, and a method of remedying soil.
2. Related Background Art
A large amount of chemical compounds or chemical products have been produced with the recent rapid progress in technology and science. Since most of these compounds or products did not originally exist in nature, they are barely decomposed naturally and thus, accumulate in the natural environment resulting in environmental pollution. In particular, land where many people live is readily affected by this artificial pollution. Since water circulates through land, the atmosphere and the hydrosphere, the environmental pollution of the land will spread globally. Well-known examples of pollutants in soil or land include organic compounds such as gasoline, organochloric chemicals such as PCB, teratogenic agrichemicals such as dioxin, as well as radioactive compounds. Fuel such as gasoline is commonly stocked in a huge amount in the underground tanks of gas stations etc. Thus, fuel leakage from deteriorated or broken tanks into soil is now a serious social problem. Further, organochloric chemicals, e.g. chlorinated aliphatic hydrocarbons such as trichloroethylene and tetrachloroethylene, were once extensively used for cleaning fine parts as well as for dry cleaning, and large scale pollution of soil and ground water due to the leakage of these chemicals has been gradually revealed. Since such organochloric chemicals are teratogenic and carcinogenic and adversely affect the biological world, remediation of the polluted soil or ground water is now an issue to be solved immediately, in addition to the isolation of the pollution source.
Methods for remedying soil polluted with these pollutants include, for example, heat treatment of the dug-up soil, vacuum extraction of the contaminant from the polluted soil, and microbial degradation of the pollutant in soil. Although the heat treatment can completely purify the soil, the soil must be dug up: thus, soil under structures cannot be purified. Moreover, it is unsuitable for large-scale treatment because of the immense costs of digging and heating. Although the vacuum extraction method is a simple and economical remediation method, organochloric compounds in a concentration of several ppm or lower cannot be efficiently removed and this remediation process requires time on the scale of years. On the other hand, microbial remediation does not require digging up of soil, so it can purify the soil under structures, and use of microorganisms of high degradation activity enables short-time remediation. Thus, this economical and effective remediation method has been attracting attention lately.
Conventional methods of remedying contaminated soil by using microorganisms can be classified into those utilizing indigenous microorganisms naturally inhabiting the soil, and those which utilize foreign microorganisms not naturally inhabiting the soil. In the former case, generally chemical substances such as nutrients, inducers and oxygen for increasing the degradation activity of the microorganisms are injected into the soil as well as microparticles such as bentonite which stimulate the growth of the microorganism (Japanese Patent Application No. 7-108678). In the latter case, the foreign microorganism is injected into the soil as well as the substances to enhance their biodegradability. For example, U.S. Pat. No. 5,133,625 describes a method in which the injection pressure, flow rate and temperature are measured by using an extendable injection pipe to control the injection pressure, thereby the concentration of microorganisms and that of nutrients in the soil, to carry out remediation of soils efficiently.
U.S. Pat. No. 5,133,625 discloses a method for efficiently remedying soil using an extensible injection pipe through which the injection pressure, flow rate, and temperature can be determined to control the injection pressure, thus to control the concentrations of microbes and nutrients in the soil. U.S. Pat. Nos. 4,442,895 and 5,032,042 disclose a method of effective in situ microbial remediation of polluted soil, where cracks are formed in the soil using a liquid or a gas injected into the soil with pressure from an injection well. U.S. Pat. No. 5,111,883 discloses a method for injecting chemicals vertically or horizontally into a limited region of the soil by setting the relative position of the injection and extraction wells.
Injection of a pollutant-decomposing microorganism, nutrients, an inducer, oxygen, and other chemicals into the soil is considered to be essential for the microbial remediation of polluted soil. However, according to the conventional injection methods, an extremely large amount should be injected to remedy a wide area, since the liquid agent is injected from the injection element to fill the soil pore space. Such a process increases the processing period, labor and material costs, resulting in increased remediation expenses. Differing from chemicals, microorganisms can spontaneously grow and multiply when certain growth conditions, such as availability of nutrients are satisfied. If a liquid agent containing the microorganism and nutrient can be injected in an amount as small as possible into a wide area of soil and the microorganism can grow in the soil to decompose pollutants, the remediation expense is considerably decreased. However, when the necessary amount of the microorganism and nutrient is injected into a wide area after dilution, the processing period and labor required for injection do not decrease. Further, a method where the liquid agent will fill most of the soil pore space may cause soil fluidization and may soften the ground. Thus, it cannot be applied to the soil under heavy structures. Moreover, the liquid agent injected into the soil penetrates into the deeper layers and diffuses into underground streams. Therefore, mobile microorganisms and nutrients will not remain within the desired area and are lost. Thus, reinjection is required, making it difficult to remedy soil at a low cost. Further, the runoff of the microorganism and nutrient may cause secondary environmental pollution. Consequently, in microbial soil remediation, an injection method is required providing a small amount of the agent into a wide area of soil without filling all the pore space of the soil.
For example, German Patent 4001320A1 describes a method for diffusing into soil a substance which can activate microorganisms, wherein a cartridge composed of an explosive directly coated with the activation substance is buried into the contaminated soil and ignited. The blast, however, is basically generated by the combustion reaction of the explosive which raises the ambient temperature to cause thermal expansion of the air around the explosive. Accordingly, the substance for activating the microorganisms might be modified or the microorganisms themselves might be debilitated or killed by the heat.